Liquid cooling system for jet engines



March 13, 1962 D. B. ADAMS ET AL LIQUID COOLING SYSTEM FOR JET ENGINES 2Sheets-Sheet 1 Filed July 10, 1958 36 as zz HU U INVENTORS P. EULLIVA-NLD B. ADAMS- ATTORNEY March 13, 1962 D. B. ADAMS ET AL LIQUID COOLINGSYSTEM FOR JET ENGINES 2 Sheets-Sheet 2 Filed July 10, 1958 INVENTORS DDNALD F. EIULLIVAN DEINALD ELADAME mww fl| ial ir|| -l illivlirsvfllv;

ATTORNEY 7 United Sates Patent 3,924,606 Patented Mar. 13, 1952 fifice3,024,606 LIQUID COOLING SYSTEM FOR JET ENGINES Donald B. Adams,Wyoming, Ohio, and Donald P. Sullivan, Van Nuys, Califi, assignors toCurtiss-Wright Corporation, a corporation of Delaware Filed .iuly 1t),1958, Ser. No. 747,608 3 Claims. (Cl. 6039.66)

This invention relates to jet engines and is particularly directed to anarrangement for cooling the walls of a hot gas or combustion chamber forsuch an engine.

In the case of a turbo-jet engine with an afterburner the Walls of theafterburner combustion chamber and exhaust duct and nozzle are subjectedto extremely high temperature gases. This is particularly true when theturbojet engine is operating at high supersonic Mach numbers. Similarlythe walls of the combustion chamber and exhaust passages of ramjet androcket engines are also subjected to high temperatures. The use of ahollow wall structure for jet engines in which liquid fuel is circulatedtherethrough prior to combustion in the engine is a known expedient formaintaining the temperature of the wall structure within safe operatinglimits. When liquid hydrocarbon fuel is so used, the fuel vaporizes andas a consequence high pressures are required to keep the fuel volumewithin reasonable limits. This is particularly true at the hightemperatures produced in the engine at high supersonic flight speeds.Furthermore, if a hydrocarbon fuel remains at too high a temperature fortoo long a period of time, it will crack, that is the more complexhydrocarbons of the fuel break up into hydrocarbons of less complexstructure. Such fuel cracking is also objectionable because along withother factors such as fuel oxidation it tends to cause coking depositsto build up along the passage walls.

An object of the invention comprises the provision of an arrangement forcooling the wall structure of a jet engine by circulating a liquidthrough passages in said wall structure and also through a heat exchangestructure for transferring heat to the jet engine fuel. This arrangementpermits the use of a cooling liquid having relatively high thermalcapacity, as for example a liquid metal such as sodium or a eutecticmixture of sodium and potassium. Also, with this arrangement, the heatfrom the cooling liquid can be rapidly transferred to the engine fuel ina heat exchange structure immediately prior to its discharge into theengine combustion chamber. This arrangement permits the use ofhydrocarbon fuels which would crack if they were used directly forcooling said wall structure because of the relatively long length oftime the fuel would require for circulation through said wall structure.

Other objects of the invention will become apparent upon reading theannexed detail description in connection with the drawing in which:

FIG. 1 is a schematic axial sectional view of a turbojet engine;

FIG. 2 is an enlarged schematic view of the afterburner and exhaust endof the turbojet engine of FIG. 1 and illustrating the invention;

FIG. 3 is an enlarged sectional view taken along line 33 of FIG. 2;

FIG. 4 is a view taken along line 4-4 of FIG. 3; and

FIGS. 5 and 6 are sectional views taken along the lines 5-5 and 66 ofFIG. 4.

Referring first to FIG. 1 of the drawing, reference numeral ltldesignates a turbojet engine having a compressor 12 supplying compressedair to a main combustion chamber 14 which in turn supplies combustiongases to the turbine 16 for driving said turbine. The combustion chamberfuel supply nozzles are shown at 18. The turbine 16 is drivablyconnected to the compressor 12 by the shaft Ztl.

From the turbine 16 the exhaust gases discharge through an exhaust duct22 and thence through a nozzle 24 into the surrounding atmosphere. Thenozzle 24 is formed by a rigid centerbody structure 26 having anenlarged plug-type end 28 and by an axially movable wall structure 30.The wall structure 30 forms a continuation of the exhaust duct 22 andhas a flared end 32 so that axial adjustment of the wall structure 30 iseffective to vary the nozzle area.

Fuel nozzles 34 and 36 are provided for supplying fuel to the exhaustduct 22 for combustion therein downstream of the fiameholder structure38 so that the space 40 downstream of said flameholder structure formsthe combustion chamber for the engine afterburner.

The details of the afterburner and nozzle end of the engine are moreclearly shown in FIGS. 2-6 together with the arrangement of theinvention for cooling the wall structure of said afterburner and nozzle.

Referring now to FIGS. 2-6 the wall structure for the outer portion ofthe afterburner chamber 40 forms a continuation of the exhaust duct 22.This wall structure comprises a hollow outer wall 42 formed by radiallyspaced annular layers 44 and 46 of sheet metal secured together by acorrugated sheet-metal member 48 disposed between said layers to form ahollow rigid wall 42. The corrugations of the member 48 are secured toand run axially between the layers 44 and 46 to form longitudinallyextending passages 50 therebetween.

The corrugated member 48 terminates short of the downstream end of thehollow wall 42 to leave an annular space 52 between its layers 44 and 46at said downstream end. An annular manifold structure 54 is provided atthe upstream end of the hollow wall 42 for supplying a liquid coolantthereto for flow through the passages 50.

The manifold structure 54 has a pair of annular inlet and outlet parts56 and 58 separated by partition means 55 such that the annular inletport 56 is in communication with only alternate passages 50 and theoutlet part 58 is in communication with only the remaining passages 59.With this construction of the manifold 54, a liquid supplied to theinlet port 56 will flow through half the passages 50 to the annularspace 52 at the downstream end of the hollow wall 42 and then flow backupstream through the remaining passages 56 to the annular outlet port 58in the manifold 54.

A pump 60 is provided for circulating a suitable cooling liquid throughthe passages 50 of the hollow wall 42. For this purpose the pump 60 hasa supply line 62 connected to the inlet port 56 of the annular manifold54. From the outlet port 58 of the manifold 54 the liquid coolant isreturned to the pump 6% through the line 64 and a heat exchangestructure 66 and thence through a line 68 back to the pump whereby saidpassages and heat exchanger from a loop passageway for circulation ofsaid liquid therearound by the pump 60. A suitable expansion chamber '70is connected to the outlet side of the pump 69 to accommodate expansionand contraction of the liquid coolant so that the hollow wall passages50 can at all times remain full of said liquid.

The afterburner fuel is supplied by a pump under control of a main fuelregulating valve 82. From the main fuel valve 82 a portion of the fuelis supplied direct to the fuel nozzles 34 via the fuel line 84. Theremaining portion of the fuel is supplied to the fuel nozzles 46 throughthe heat exchange structure 66, valve 86 and fuel line 88. Theafterburner fuel nozzles 3.6 aredisposed but a short distance upstreamof the flameholder structure 38. The afterburner fuel nozzles 34,however, are disposed a substantial distance upstream of the fuelnozzles 36 and the afterburner flameholderstructure 38.

The valve 82 regulates the total fuel supply to the afterburner fuelnozzles 34 and 36 while the valve 86 regulates the division of fuel flowbetween said nozzles. The valve 86 preferably is automaticallycontrolled by the temperature of the fuel as it leaves the heatexchanger 66 such that during operation the temperature of the fuel, asit leaves the heat exchanger 66, is maintained at least approximately ata predetermined value, for example 900 F. Thus any increase in saidtemperature above 900 F. results in opening adjustment of the valve 86so that a larger percentage of the fuel is diverted through the heatexchanger 66. In this way the valve 86 is automatically operative toprevent the temperature of the fuel supplied thru the heat exchanger 66from exceeding a predetermined value. Temperature control of the valve86 is schematically indicated as comprising a conventional fluid filledtemperature responsive bulb 90 in the fuel line 38 at the heat exchanger66. The bulb 90 is connected to a bellows 92 which in turn ismechanically connected to the valve 86 so that an increase in fueltemperature at the bulb 90 results on opening adjustment of said valveagainst the spring 94.

With the structure described, circulation of the liquid coolant throughthe passages 50 of the afterburner hollow wall 42 serves to keep thetemperature of said wall below a maximum safe value. The heat absorbedby the liquid coolant is extracted in the heat exchanger 66 by the fuelflowing therethrough in heat exchange relation to said coolant. Thisfuel is heated to a sutficiently high temperature in the heat exchanger66 so that it vaporizes therein or it at least vaporizes promptly uponbeing discharged into the afterburner from the downstream fuel nozzle36. The fuel nozzles 34 are disposed a substantial distance upstream ofthe flameholder structure 38 so as to give this unheated portion of thefuel time to vaporize and mix with the turbine exhaust gases beforereaching the fiameholder.

The cooling liquid circulated through the passages 50 of the hollowafterburner wall 42 preferably is a metal which is in the liquid stateat the temperatures of the turbine exhaust. Hence the coolant metal willbecome a liquid before the engine after-burner is started. A suitablemetal for this purpose is an eutectic mixture of sodium and potassium.Other metals such as pure sodium may also be used. Such a liquid coolanthas the advantage of a high thermal capacity so that it will absorb alarge amount of heat with a relatively small temperature rise.

If a hydrocarbon fuel were used directly as the fluid coolant in thepassages 50 it would vaporize therein and would require large pressuresto keep the volume of the fuel required for cooling within reason. Thiswould mean that with a hydrocarbon fuel as the coolant for the passages50, the walls of said passages would have to be strong enough towithstand much higher pressures than is required when a liquid metalliccoolant is so used. Also because of the large surface area of the hollowwall structure 42 required to be cooled a substantial time is requiredfor circulation of the coolant thru its passages 50. Hence if ahydrocarbon fuel were used as a coolant in these passages the fuel wouldtend to crack because of the temperature the fuel would attain andbecause of the length of time the fuel would be at this temperature.Such cracking is objectionable because it changes the structure of thefuel and in addition fuel cracking along with other factors such as fueloxidation in the passages 50 would tend to cause coking deposits tobuild up along the walls of said passages.

By using a liquid metal coolant to cool the hollow wall 42 and thentransferring the heat from the liquid coolant to the fuel in the heatexchanger 66, the heat can be transferred rapidly to the fuel so thatthe fuel is at a high temperature for only a short period of time beforeit is discharged into the engine afterburner at the fuel nozzles 36.With this arrangement the length of time the fuel is at the hightemperature before burning in the afterburner can be kept sufiicientlyshort to minimize cracking of the fuel.

In order to minimize the heat transfer from the afterburner combustiongases to the liquid coolant in the hollow wall passages 50, the wallstructure for the outer portion of the afterburner chamber 40 alsoincludes a heat barrier or insulating layer disposed over the innersurface of the hollow wall 42. The heat insulating layer preferably isof a sheet metal honeycomb construction having an inner cylindricalshell 102 with a honeycomb structure 104 disposed between said shell andthe hollow wall 42. The inner shell 102 has longitudinally extendingcorrugations 106 to facilitate expansion and contraction of said shell.The walls of the honeycomb structure 104 have openings 108 so that thecells of said structure are interconnected. These interconnected cellsare vented to the surrounding atmosphere for example by the passageindicated at 110.

The honeycomb layer 100 prevents the heat loss from the afterburnergases to the liquid coolant in the passage 50 of the hollow wall 42 frombecoming excessive. Also because of the corrugations 106 the layer 100will tend to expand with internal pressure so that it transmits theinternal pressure to the liquid cooled hollow wall 42. With thisarrangement the relatively cool outer wall 42 carries all the structuralloads while the inner wall or layer 100 not only acts as a heat barrierbut, because of its resiliency, also acts to transfer the internal gaspressure loads to the cool outer wall. Having the loads all carried bythe relatively cool wall 42 minimizes the required weight of theafterburner wall structure.

The wall structure of the centerbody 26 and plug 28 and that of theaxially movable wall 30 are all subjected to the hot afterburner gases.Each of these wall structures, like that for the outer portion of theafterburner combustion chamber 40, includes a hollow liquid cooled walltogether with a honey-comb layer disposed over said hollow wall tofunction as a heat barrier.

In the case of the centerbody 26, the hollow wall of said centerbody hasan outlet annular manifold 122 at one end and an inlet annular manifold124 adjacent the maximum diameter portion of the plug 28. The pump 60 isconnected to the inlet manifold 124 by a line 126 and a line 128 returnsthe coolant from the outlet manifold 122 to the return line 64. In thisway all the liquid coolant supplied to the manifold 124 flowslongitudinally through passages (similar to the passages 50) in thehollow wall 120 to its outlet manifold 122 to cool said well.

Liquid coolant is also supplied by the line 126 to an inlet manifold 130at the rear end of the plug 28 from which it flows through passages(similar to the passages 50) in its hollow wall 132 to an outletmanifold 134 which is connected to the return line 128.

Likewise liquid coolant is supplied by the pump 60 and supply line 142to an annular inlet manifold 144 disposed at a mid or intermediate pointalong the hollow wall 146 of the movable wall structure 30. The inletmanifold 144 communicates with only alternate passages (similar to thepassages 50) in the hollow wall 146 and only with the portion of saidpassages along the upstream portion of said wall. A partition 148 isdisposed across only these alternate passages at said mid orintermediate point. An annular outlet manifold 150 is disposed adjacentto the inlet manifold and communicates with only the same alternatepassages as the inlet manifold but on the other side of the partition148. Liquid supplied to the inlet manifold 144 flows through saidalternate passages to an annulus 152 at the upstream end of the hollowwall 146 and thence through the other passages in the hollow wall 146 toan annulus 154 at its downstream end and then through the firstmentioned alternate passages to the outlet manifold 150 which in turncommunicates with the return line 64.

Since the wall 30 is axially movable the connections to the manifolds144 and 150 are flexible as schematically indicated on the drawing at160 and 162 respectively. Linkage 164 is connected to the wall 38 foraxially adjusting its position to vary the nozzle area.

The hollow walls 120, 132, and 146 are provided with heat barrier layers166, 168, and 170 respectively of honeycomb construction similar tolayer 101 of the hollow wall 42. Actually the outer wall structure ofthe afterburner chamber 40, the wall structure of the centerbody 26,plug 28, and movable wall 38 essentially are all the same. The onlydiiferences lie in the various manifold arrangements described forcirculating the liquid coolant through their hollow walls.

While we have described our invention in detail in its present preferredembodiment it will be obvious to those skilled in the art afterunderstanding our invention that various changes and modifications maybe made therein without departing from the spirit or scope thereof.

We claim as our invention:

1. In combination with a jet engine having a chamber thru which theengine combustion gases flow at substantial velocity, said chamberhaving a hollow wall providing a rigid wall structure with a pluralityof passages therethru; means providing a loop passageway including saidhollow wall passages; a coolant within said loop passageway forcirculation therearound for cooling said hollow wall, said coolant beinga metal which is in the liquid state during engine operation; two nozzlestructures for discharging fuel into said engine for combustion thereinand flow of the combustion gases thru said chamber, said two nozzlestructures being spaced so that one is disposed a substantial distancedownstream of the other; a common source of fuel having passageconnections to both said nozzle structures; a heat exchange structureinterposed in the flow path of said liquid coolant to and from saidchamber Wall and in the flow path of fuel flow from said common sourceonly to the downstream one of said two nozzle structures for flow ofsaid latter fuel and liquid coolant thru said heat exchanger in heatexchange relation for transferring heat from said liquid coolant to thefuel supplied to the downstream nozzle structure; and

means for regulating the division of fuel flow from said common sourceto said two nozzle structures.

2. The combination claimed in claim 1 and in which said last mentionedmeans comprises valve means; and means responsive to the temperature ofthe fuel leaving said heat exchange structure and operatively connectedto said valve means for increasing the fuel flow thru said heat exchangestructure should said temperature exceed a predetermined value.

3. The combination recited in claim 2 in which said wall constructionhas an inner layer providing a heat barrier between said hot gases andsaid rigid hollow wall, said inner layer having a honeycomb constructionwith an inner shell closing the cells of said honeycomb to the hotgases, said inner shell having corrugation to permit outward expansionthereof.

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